The November 25 naval skirmish between Russian and Ukrainian forces in the Kerch Strait was significant first and foremost as an open military confrontation between the two countries’ armed forces. But it also highlighted the fraught legal status of the strait and the Azov Sea, a status that Russia has been exploiting in recent months to exert political and economic pressure on Ukraine.

A slow march to confrontation

The confrontation began months before the recent events that brought the conflict to worldwide attention. In March 2018, Ukrainian border guard vessels detained a Russian fishing vessel in the Azov Sea for violating exit procedures from the “temporarily occupied territory of Ukraine”, namely from Crimea. The crew of that vessel remained in detention for several months, until they were exchanged in October for Ukrainian sailors. The captain of the Russian ship remains in Ukraine and is facing prosecution for illegal fishing and “violation of the procedure for entry and exit from the temporarily occupied territory of Ukraine”. Since that incident, Russia has retaliated by detaining several Ukrainian fishing vessels.

In May, Russia also began to regularly hold Ukrainian commercial ships for inspection before allowing them to pass through the Kerch Strait. The initiation of this inspection regime largely coincided with the opening of a road and rail bridge across the strait. Russia claimed that the inspections were required to ensure the safety and security of the bridge at a time when some Ukrainians had publicly threatened to attack the bridge. The delays caused by the inspection regime, together with ship height restrictions caused by the bridge, have led to a 30 percent reduction in revenues at Ukraine’s commercial ports of Mariupol and Berdyansk, raising fears that Russia is trying to strangle the economy of eastern Ukraine.

In the same period, Russia also began to build up its naval presence in the Azov Sea, with at least three missile ships based there since summer 2018. Reports indicate that Russia plans to set up a full-fledged flotilla in the Azov in the near future. Ukraine has also strengthened its naval presence in the region, placing several armoured boats in Berdyansk and seeking to expand the base there.

The transfer of ships from Odesa to Berdyansk that caused the skirmish was part of this effort. Ukraine had moved naval ships through the Kerch Strait as recently as September 2018, but these ships were not armed. In that case, the ships were allowed to pass through without incident, although they were closely followed by Russian border guard vessels. The passage of two armoured boats through the strait in late November was thus the first attempt by the Ukrainian Navy to bring armed ships through the Kerch Strait since tensions began to mount and the bridge was completed in spring 2018.

The legal background

The status of the Azov Sea and the Kerch Strait is regulated by a bilateral treaty that was signed by Russia and Ukraine in 2003. According to the terms of the treaty, the sea is considered to be internal waters for both countries, and both Ukrainian and Russian commercial and military ships have the right of free passage through the strait. Furthermore, the treaty does not specify any particular advance notice procedures for passage through the strait. Foreign commercial ships are allowed to pass through the strait and enter the sea if they are heading to or from a Ukrainian or Russian port. Military ships belonging to other countries may be allowed passage if they are invited by one of the signatories to the treaty, but only with the agreement of the other signatory. In 2015, Russia unilaterally adopted a set of rules requiring ships passing through the strait to give advance notification to the Russian authorities, ostensibly to assure safety of navigation. These rules have not been accepted by Ukraine.